Method and device for controlling the transition between normal operation and overrun fuel cut-off operation of an otto engine operated with direct fuel injection

Abstract

The problem during overrun fuel cut-off operations, i.e. cut-off of fuel injection during trailing throttle conditions of the vehicle, is that the transition entails an undue torque jump, resulting in the smooth operation of the engine and the driving comfort of the passengers of the vehicle being affected. The aim of the invention is to reduce the torque jump. Said aim is achieved by injecting fuel into a cylinder of the Otto engine in a multiple injection process, at least a partial quantity of the fuel that is to be injected being injected during the compression phase, whereby the quantity of air that is taken in advantageously decreases because no internal cooling takes place while the efficiency is advantageously reduced due to the lesser degree of swirling, resulting in lower torque. Overall, torque (DM) is reduced to a significantly greater extent than by merely adjusting the spark angle (ZW) while smooth operation of the Otto engine is not affected.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application is the US National Stage of International Application No. PCT / EP2004 / 050572, filed Apr. 21, 2004 and claims the benefit thereof. The International Application claims the benefits of German application No. 10334401.2 filed on Jul. 28, 2003. All of the applications are incorporated by reference herein in their entirety.FIELD OF THE INVENTION [0002] The invention takes as its starting point a method or an apparatus, whereby the transition between normal operation and overrun fuel cut-off operation can be controlled in an Otto engine which is operated with direct fuel injection. BACKGROUND OF THE INVENTION [0003] When switching over from the normal operation to the overrun fuel cut-off operation, there is inevitably a torque jump which can cause an irregular running of the Otto engine or an unwanted judder of the vehicle. The advantages which per se derive from the overrun fuel cut-off, such as a reduction in the fuel consu...

AI Technical Summary

Benefits of technology

[0007] In the claimed method or the apparatus for controlling the transition between normal operation and overrun fuel cut-off in an Otto engine which is operated with direct fuel injection, said method and apparatus having the characterizing features of the respective claims, the advantage emerges that the torque reduction is essentially greater than if solely the ignition angle is adjusted. This is because, as a result of injecting at least a partial quantity of the fuel during the compression phase, three beneficial effects are produced for curbing the torque. Firstly, the mass of air that is taken in decreases due to the reduced internal cooling in the cylinder, because part of the injected fuel quantity is injected at the time point when the valves of the cylinder are already closed (compression phase). Secondly, the efficiency of the combustion decreases because the fuel which is in the cylinder is swirled less vigorously when injection takes place in the compression phase. Finally, measurements have also shown advantageously that the smooth running of the Otto engine does not change if the ignition angle is adjusted even further in the retard direction after the injection of fuel. Consequently, the injection angle can be adjusted even further in the retarded injection direction than would be the case in the known simple adjustment of the injection angle. It is further considered particularly advantageous that the torque jump can be reduced in a manner which is essentially more effective by means of the claimed method or by means of the apparatus, such that the advantages of the overrun fuel cut-off can be utilized without the driving comfort for the passengers of the vehicle being adversely affected by the torque jump.

[0009] After the minimal ignition angle has been reached, the fuel is injected into the cylinder during the compression phase when the valves are closed. This is contrary to the otherwise usual procedure, in which the fuel is injected in the intake phase, i.e. when the valves are open. In the claimed method therefore, the advantage is produced that the ignition angle can be decreased even further than would have been the case in the known ignition angle adjustment. The ignition angle can now be decreased to a second minimal value, which is lower and applies to the multiple injection, since the fuel-air mixture in the cylinder remains combustible.

[0011] When the vehicle is switched over from overrun fuel cut-off operation to normal operation, a check first ascertains whether it is necessary to carry out the injection. If this is the case, the fuel to be injected is deposited in the compression phase. As a result, the torque is slowly built up and an unwanted torque jump is avoided.

Problems solved by technology

Firstly, the mass of air that is taken in decreases due to the reduced internal cooling in the cylinder, because part of the injected fuel quantity is injected at the time point when the valves of the cylinder are already closed (compression phase).

Secondly, the efficiency of the combustion decreases because the fuel which is in the cylinder is swirled less vigorously when injection takes place in the compression phase.

Images